This invention relates to magnetron apparatus comprising a magnetron tube and a circuit for driving the same, and more particularly an improved magnetron construction capable of preventing leakage of undesired high frequency wave from the power input of the magnetron.
In a microwave oven or the like utilizing magnetron apparatus, high frequency energy is generally used so that it is important to prevent leakage of the electromagnetic wave which affects television and radio receiver sets. More particularly, as will be described later in detail with reference to the accompanying drawings, a portion of the high frequency energy created in the interaction space of the magnetron tube during the operation thereof is captured by the cathode filament located in the interaction space and it leaks to the outside of the tube through filament lead wires. Since such leaked wave interferes with the operation of various communication devices, it is necessary to prevent such leakage. To accomplish this, in one example of the prior art magnetron, a metal shield is mounted on a magnetron tube so as to surround the cathode filament terminals of the magnetron tube and a wave leakage prevention filter comprising a coil and a serially connected feed-through capacitor is connected between the filament terminals and lead wires led from the shield casing and extending to an external source.
However, since the operating voltage of the feed-through capacitor is a high voltage which is substantially equal to the anode voltage of the magnetron tube, it is necessary for the feed-through capacitor to withstand against such a high voltage and hence the feed-through capacitor is expensive. Due to a limit on the size of the coil and feed-through capacitor and the insulating strength required for the feed-through capacitor, the cut-off frequency of the filter becomes to about several MHz so that the filter is not effective to prevent leakage of the waves having a frequency less than this frequency.